1. Field of the Invention
The present invention relates to s multilayer class identifying communication apparatus used in an IP network of a network layer of an OSI reference model.
2. Description of the Related Art
Recently, the Internet, which is regarded as a de facto standard, has been standardized as a global network, based on Transmission Control Protocol/Internet Protocol (TCP/IP). Usually, in the seven layers of the OSI reference model, the IP serves as the network layer, and the TCP serves as the transport layer. Data is passed from the lowest layer Ethernet and token-ring network to the IP and passed from the TCP to the application layer.
A router as a relay device between local-area networks (LAN) is arranged between a repeater, a bridge, and a gateway. The router is used to accumulate frames sent from a communication line and transmit them to an appropriate communication line according to a network address included in the data of the frames.
A conventional router fairly handles all IP packets and basically does not perform priority control over IP packets. Each IP packet includes an IP address in its header and stays in a buffer of the router. Since the IP packet is read from the buffer by the first-in first-out (FIFO), no delay priority control is performed. When the IP packets converge to a certain output port, congestion occurs, thereby causing the discard of packets in the buffer of the router. Usually, no priority control is performed over the discard of packets.
In contrast, the known ATM technology introduces the concept of connection, in which a route connecting a source address and a destination address is clearly defined by a virtual path identifier/a virtual channel identifier (VPI/VCI). This concept permits the quality of service (QOS) such as delay characteristics and discard ratios, which is necessary for a connection unit to be defined. In addition, network apparatuses perform priority controls so that the QOS of connections are satisfied.
(IP-QOS)
Consideration is now given to technologies for easily performing priority control on the Internet. Typical examples are Intserve/Resource Reservation Setup Protocol (RSVP) as a protocol for performing the network band control, and Differentiated Service. The former simulates the concept of connection as introduced in the ATM, while the latter performs priority control based on packet data as much as possible.
The Intserve/RSVP system is not applicable to a large-scale backbone network at low cost. That is, the system lacks scalability, and it is thereby not widely used. In order to solve the problem, the Differentiated Service primarily considers scalability, availability at low cost, and adaptability to the high-speed performance of an optical carrier (OC)-48 class as an interface for a backbone network optical fiber according to transmission velocities.
The Differentiated Service guarantees quantitative service as in the ATM-QOS. Instead, from the viewpoint of the best effort, the Service sets a relative quality difference to facilitate the differentiation of service. This is accepted as a substantially practical solution judging from specification progress by the Internet engineering task force (IETF) as a Net-problem solving organization and vendor responses.
(Differentiated Service)
The Differentiated Service system has been discussed in the IETF, which regulates the Internet technologies. The Differentiated Service is a system for differentiating service levels, and does not guarantee the QOS. This is strictly for a relative priority control framework. That is, the Differentiated Service only defines the frameworks of QOS classes. The details of the QOS classes and scheduling formats between the QOS classes are referred to vendors and users.
(Service Classes in the Differentiated Service)
The Differentiated Service has three kinds of defined traffics (service classes) including an expedited forwarding service (EF class) as a premium service, an assured forwarding service (AF class), and a best effort service (BE class). The premium expedited forwarding (EF) class provides a virtual dedicated-line service such as an IP-CBR (constant bit rate) on an IP network. Thus, it is necessary to perform precise transmission control including usage parameter control (UPC) by additionally using a shaping section. Since the EF class is regarded as a class for a band guarantee service, it takes first priority over the assured forwarding service (AF class) and the best effort service (BE class), which will be described below.
Unlike the expedited forwarding (EF) class as the premium class, the assured forwarding service (AF) class is only for a relative priority control framework. The assured forwarding service has four kinds of delay classes and three kinds of discard classes. Delay priority control is performed by giving priority to an order in which IP packets in a network apparatus are transmitted. For example, this is effective in reducing the transmission delay of an application responsive to delay. Discard control is performed by giving priority to the discarding of packets in a place where congestion occurs in the network apparatus. The best effort service (BE class) is applied as a third traffic, besides the EF class and the AF class. Of the service classes, the lowest priority control is given to the BE class.
The above description outlines the Differentiated Service. However, the recommendation of the Differentiated Service is still in a state of flux. Thus, the definitions and usage described above can be changed.
In conjunction with the above description, a packet transmitting and receiving node is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 2-87747). In this reference, the packet transmitting and receiving node is composed of a reception buffer, a header analyzing section, a reception packet storing section, a passage packet storage and analysis section, a generation packet storage and analysis section, a control section and a transmission switch. The reception buffer stores reception packets. The header analyzing section analyzes a destination and a service class from a header of each of the reception packets stored in the reception buffer. The reception packet storage section stores the reception packets from the reception buffer when the reception packets are destined to the node. The passage packet storage section stores the reception packets from the reception buffer when the reception packets are destined to other nodes. The generation packet storage analysis section stores and analyzes packets to be sent from the node to other nodes for every service class. The control section is given the number of packets and a packet generation time as the analysis results of the passage packet storage and analysis section and the number of packets and a packet generation time as the analysis results of the generation packet storage and analysis section, when referring to a priority level predetermined for the passage packet storage and analysis section and the generation packet storage and analysis section to determine a transmission order of the packets from the storage and analysis sections, and determines whether the number of packets stored in each storage and analysis section exceeds a predetermined storage limitation packet count and whether the difference between the packet generation time and a present time exceeds a predetermined delay limitation time for every storage and analysis section. The control section determines that the packet should be primarily sent with no relation to the priority level of the packet when the packet generation time or the number of packets exceeds the limitation. The transmission switch takes out the packet from the storage and analysis section to transmit it.
Also, a packet switching apparatus is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 5-191455). In this reference, a routing operation to the whole packet switching network is carried out based on priority classes. A buffer is provided for every priority class, which is separately and independently allocated with a delay and a discard rate as a transmission quality. Packets stored in the buffer from a transmission line in relaying of packets are subjected to a classifying process of the packets. The number of packets after the classification is monitored and an estimation delay is calculated for every priority class. The packets with permissible long delays are set to have long routes for load distribution when load is rapidly increased. Packets with large discard rates are discarded. The packet switching apparatus is composed of line accommodating section and a control section. The line accommodating section has a routing table indicative of a route and discard instruction for every priority class for the above operations. The control section updates the routing table for every priority class based on delay data from the line accommodating section and switching apparatus status data of other stations.
Also, a switching apparatus is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 7-154421). In this reference, data packets for at least two different priority classes are stored in buffers, respectively. Each of the buffers is allocated with a threshold value. The threshold value for a higher priority class is equal to or higher than that for a lower priority class. When a packet newly arrives the buffer, the priority level of the packet and an occupation rate of the buffer are determined. The occupation rate is compared with the threshold value for the buffer and the packet is stored in the buffer or discarded based on the comparing result. At least threshold value is dynamically controlled.
Also, a cell transfer control method is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 9-205441). In this reference, when a connection belong to a specific traffic class with no band reservation is established, a discard priority data notified from a generation unit is stored in a node unit in correspondence to an identifier of the connection. A cell belonging to the specific traffic class is selectively discarded based on a predetermined discard condition which is determined a congestion state and the priority level when the route for the connection is in the congestion state.
Also, a transmission traffic control apparatus is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 10-23012). In this reference, a data is transmitted in a fixed length packet or cell. A transmission traffic control apparatus is connected to a virtual path (VP) switch network and is composed of a header converting section, a control section, a transmission scheduler, and a read control section. The header converting section allocates an output side VPI/VCI value, which has been determined upon the establishment of the connection, and a class identifier corresponding to an in-apparatus class to a reception cell. The control section classifies the reception cell based on the VPI value and the class identifier given to an in-apparatus header to write a class queue. There are a usual class buffer and a variable class buffer. The transmission scheduler controls the maximum rate for every VP and a rate of the variable queue. The read control section reads out data from the class queue in response to an instruction from the transmission scheduler. The variable buffer includes a forward resource managing cell (FRM cell) inserting section for inserting a FRM cell. A receiving side apparatus connected via the VP switch network is composed of an FRM cell extracting section for extracting the FRM cell which has been inserted, means for monitoring the content of EFCI based on the content of the reception cell for every VP, a EFCI register for holding a latest EFCI data, a function for stamping the content of the EFCI resister on a congestion indication bit (CI) of a backward RM cell (BRM cell), and a BRM cell inserting section for inserting the BRM cell in a downstream. The transmission scheduler is composed of means for controlling the maximum rate for every VP, a control parameter, various parameters for controlling the variable class queue rate, and means for controlling the insertion of the FRM cell and the monitoring the reception of the BRM cell. Also, the transmission scheduler has a function to control a variable transmission rate in accordance with the reception of the RM cells and the congestion indication bit, and allocates a priority having a relation of (normal class)>(FRM cell)>(variable class) in a range to the maximum rate for every VP.